The catalytic reduction of NOx under different oxygen concentrations leading to different NO/NO2 compositions has been studied in the presence of V3W9Ti and V8W9Ti catalysts in a tubular flow reactor. The results have shown that increasing O2 concentration leads to increase the NOx reduction in low temperature range [150-275 °C]. Slight effect of O2 concentration on NOx conversion was observed at higher temperatures. SCR reaction also occurred in the absence of gaseous oxygen but with low NO conversion indicating the strong redox properties of both catalysts. Aged catalysts exhibited relative good activities in NOx reduction. This is probably due to the sol gel method used for the preparation of the catalysts known to improve the catalysts properties.